I will summarize what I have just been saying. When we are sleeping naturally, it is not necessary to believe, as has often been supposed, that our senses are closed to external sensations. Our senses continue to be active. They act, it is true, with less precision, but in compensation they embrace a host of "subjective" impressions which pass unperceived when we are awake--for then we live in a world of perceptions common to all men--and which reappear in sleep, when we live only for ourselves. Thus our faculty of sense perception, far from being narrowed during sleep at all points, is on the contrary extended, at least in certain directions, in its field of operations. It is true that it often loses in energy, in _tension_, what it gains in extension. It brings to us only confused impressions. These impressions are the materials of our dreams. But they are only the materials, they do not suffice to produce them. They do not suffice to produce them, because they are vague and indeterminate. To speak only of those that play the principal role, the changing colors and forms, which deploy before us when our eyes are closed, never have well-defined contours. Here are black lines upon a white background. They may represent to the dreamer the page of a book, or the facade of a new house with dark blinds, or any number of other things. Who will choose? What is the form that will imprint its decision upon the indecision of this material? This form is our memory. Let us note first that the dream in general creates nothing. Doubtless there may be cited some examples of artistic, literary and scientific production in dreams. I will recall only the well-known anecdote told of Tartini, a violinist-composer of the eighteenth century. As he was trying to compose a sonata and the muse remained recalcitrant, he went to sleep and he saw in a dream the devil, who seized his violin and played with master hand the desired sonata. Tartini wrote it out from memory when he woke. It has come to us under the name of "The Devil's Sonata." But it is very difficult, in regard to such old cases, to distinguish between history and legend. We should have auto-observations of certain authenticity. Now I have not been able to find anything more than that of the contemporary English novelist, Stevenson. In a very curious essay entitled "A Chapter on Dreams," this author, who is endowed with a rare talent for analysis, explains to us how the most original of his stories have been composed or at least sketched in dreams. But read the chapter carefully. You will see that at a certain time in his life Stevenson had come to be in an habitual psychical state where it was very hard for him to say whether he was sleeping or waking. That appears to me to be the truth. When the mind creates, I would say when it is capable of giving the effort of organization and synthesis which is necessary to triumph over a certain difficulty, to solve a